The present invention relates to vehicle navigation systems, and, more particularly, to a system for guiding a vehicle along an optimal route computed beforehand.
Generally, a vehicle navigation system computes from map data the optimal route from a starting point to a destination before starting a journey. En route, the system computes local directions along the optimal route with reference to the vehicle's present location in real time. The system guides the vehicle's navigation from a starting point to a destination by displaying route information in real time on a CRT.
When a vehicle travels, the driver may overlook navigational guidance on the display and thereby deviate from the optimal route. In such cases conventional navigation systems call either for bringing the vehicle back to the optimal route, a necessary condition before navigational guidance can be resumed, or, as described in Japanese Laid-Open Patent Publication No. 51015/1990, for manually activating recomputation of a new optimal route.
However, it is difficult for a driver who is unfamiliar with a local road network to return to the optimal route once he has strayed from it. It is also a considerable inconvenience for a driver to recompute the optimal route while driving.